1. Field of the Invention
The invention relates to a technique for improving drivability in a vehicle that includes an engine having a supercharger and an automatic transmission.
2. Description of Related Art
There has been widely known a vehicle driving control system that is used in a vehicle that includes an engine having a supercharger and an automatic transmission. For example, a vehicle control system described in Published Japanese Translation of PCT Application No. 2005-500944 (JP 2005-500944 A) is such a vehicle driving control system. The vehicle driving control system described in JP 2005-500944 A keeps a supercharging pressure while decreasing an engine torque at the time of an upshift of the automatic transmission. Thus, accelerating performance after the upshift is improved.
Incidentally, various controls are known as control for decreasing an engine torque. For example, there are known ignition retardation torque reduction control for decreasing an engine torque by retarding the ignition timing of the engine, throttle torque reduction control for decreasing an engine torque by reducing the opening degree of a throttle valve of the engine, and the like. These controls for decreasing an engine torque are executed in order to reduce a shift time, absorb a shock at an inertia phase and reduce a load of a clutch, and the like, of the automatic transmission, for example, at the time of an upshift of the automatic transmission.
However, in the case where engine torque is decreased at the time of an upshift of the automatic transmission, even when the supercharging pressure is tried to be kept at a target value, it has been assumed, that it may be not possible to appropriately keep the supercharging pressure at the target value due to a difference in method of decreasing an engine toque in torque reduction control, selected at that time. For example, when engine torque is decreased by executing the throttle torque reduction control while execution of the ignition retardation torque reduction control is restricted, it may deteriorate drivability due to a decrease in supercharging pressure.
In addition, it is not clear in JP 2005-500944 A how an engine torque is decreased at the time of an upshift, but, for example, if an engine torque is decreased at the time of the upshift by executing the ignition retardation torque reduction control, the exhaust temperature of exhaust gas from the engine rises due to ignition timing retardation of the engine in the ignition retardation torque reduction control, and the durability of the supercharger may be impaired due to a rise in temperature. On the other hand, it is conceivable that the durability of the supercharger is ensured when the heat-resistant temperature of the supercharger is raised; however, in such a case, a high heat-resistant material is employed for the supercharger, which conceivably leads to an increase in the cost of the supercharger. Such inconveniences are not in public domain.